TAT-1 (Transatlantic No. 1) was the first submarine transatlantic telephone cable system. It was laid between Oban, Scotland and Clarenville, Newfoundland.[1] Two cables were laid between 1955 and 1956. One cable for each direction.[1] It was inaugurated on September 25, 1956.[2] The cable was able to carry 35 simultaneous telephone calls.[3] A 36th channel was used to carry up to 22 telegraph lines.[3]
The first transatlantic telegraph cable had been laid in 1858 (see Cyrus West Field).[4] It only operated for a month, but was replaced with a successful connection in 1866.[4] A radio-based transatlantic telephone service was started in 1927. It charged £9 for three minutes.[5] A telephone cable was discussed at that time. But it was not practical until a number of technological advances arrived in the 1940s.
The developments that made TAT-1 possible were coaxial cable, polyethylene insulation, very reliable vacuum tubes for the submerged repeaters and an improvement in carrier equipment. Transistors were not used, being a recent invention of unknown longevity.